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机械工程英语叶邦彦第二单元到第四单元课文+翻译.docx

1、机械工程英语叶邦彦第二单元到第四单元课文+翻译Unit 2 Numerical Control of Production EquipmentUnit 2 生产设备的数字控制Numerical Control (NC) is a form of programmable automation in which the processing equipment is controlled by means of numbers, letters, and other symbols. The numbers, letters, and symbols are coded in an approp

2、riate format to define a program of instructions for a particular work-part or job. 数控是程序控制的自动化,在数字控制系统中,设备通过数字,字母和符号来编码,以一种合适的格式为每一个特定的零件或工件定义一个程序指令集。When the job changes, the program of instructions is changed. The capability to change the program is what makes NC suitable for low-and medium-volum

3、e production. It is much easier to write new programs than to make major alterations of the processing equipment.当工件变化时,程序也变化,改变程序的能力亦适合中小批量生产。写一个新程序比改变大量生产设备要容易的多。Basic Components of NC数控基本结构A numerical control system consists of the following three basic components:数控系统由下面三部分组成: Program of instruc

4、tions控制程序 Machine control unit机器控制单元 Processing equipment加工设备 The general relationship among the three components is illustrated in Fig. 2.1. The program is fed into the control unit, which directs the processing equipment accordingly. 三部分的基本关系,由图2.1 所示。程序输入到控制单元由送入的程序来引导加工设备控制。 The program of instr

5、uction is the detailed step-by-step commands that direct the processing equipment. 指导程序是一步步详细的指导加工设备的指令。 In its most common form, the commands refer to positions of a machine tool spindle with respect to the worktable on which the part is fixtured. 通常指令把主轴上刀具相对于安装工具的工作台定位。More advanced instructions

6、include selection of spindle speeds, cutting tools, and other functions. The program is coded on a suitable medium for submission to the machine control unit. 更多先进的说明包括主轴的转速,加工工具的选择及其功能。The most common medium in use over the last several decades has been 1-in.-wide punched tape. 程序刻在合适的介质中,提交到机器控制单元

7、中,在过去几十年中,最常用的介质是一英寸宽的打孔纸带。Because of the widespread use of the punched tape, NC is sometimes called “tape control”. However, this is a misnomer in modern usage of numerical control . 由于打孔纸带的广泛使用,NC 有时也叫纸带控制,然而这是现代数控使用的误称。Coming into use more recently have been magnetic tape cassettes and floppy dis

8、kettes. 现在进入使用更多的是磁带和软盘。 The machine control unit (MCU) consists of the electronics and control hardware that read and interpret the program of instruction and convert it into mechanical actions of the machine tool or other processing equipment. 机器控制单元(MCU)由电子和控制硬件组成,机器控制单元可以读出和执行指令程序,可以自动改变加工工具和其他加

9、工设备。 The processing equipment is the third basic component of an NC system. It is the component that performs useful work. 执行单元是数控系统的第三基础部分,执行原件是有效执行工作的原件 In the most common example of numerical control, one that performs machining operations, 最常见的数控例子其中的一个加工操作,加工设备由工作台和主轴组成,就像用电动机来驱动一样。the processi

10、ng equipment consists of the workable and spindle as well as the motors and controls needed to drive them. 加工设备由控制单元来驱动控制系统的类型。Types of Control Systems控制系统的类型There are two basic types of control system in numerical control : point-to-point and contouring. In the point-to-point system, also called po

11、sitioning, each axis of the machine is driven separately by leadscrews and, depending on the type of operation, at different velocities. 数控有2 种基本类型,点对点式和轮廓式控制,点对点式控制也称定位控制,每个轴都是通过丝杠单独驱动,根据加工类型不同,加工速度也不一样。 The machine moves initially at maximum velocity in order to reduce nonproductive time but decel

12、erates as the tool reaches its numerically defined position. 样。机器开始以最大速度运行来减少非加工时间,但当他达到数据定义的位置时,机器开始减速。 Thus in an operation such as drilling or punching, the positioning and cutting take place sequentially. 因此在一个操作中,如钻或冲孔操作先定位在加工。 After the hole is drilled or punched, the tool retracts, moves rapi

13、dly to another position, and repeats the operation. 在钻或冲孔之后,迅速收起工具移动到另一个位置重复此操作。The path followed from one position to another is important in only one aspect: The time required should be minimized for efficiency. 从一个位置移到另一个位置是非常重要的,要遵循一个原则,从效率上考虑只要时间最短即可。Point-to-point systems are used mainly in dr

14、illing, punching, and straight milling operations. 点对点系统主要用于钻,冲孔,直铣操作中。 In the contouring system, also known as the continuous path system, positioning and cutting operations are both along controlled paths but at different velocities. Because the tool cuts as it travels along a prescribed path, acc

15、urate control and synchronization of velocities and movements are important. 轮廓式也就是连续路径式系统,定位和切削同时按不同速度来控制,由于刀具在指定路线运动同时切削,因此速度和运动的同步控制是非常重要的。The contouring system is used on lathes, milling machines, grinders, welding machinery, and machining centers. 轮廓式系统常用于车床铣床磨床焊接设备和加工中心。 Movement along the pat

16、h, or interpolation, occurs incrementally, by one of several basic methods. In all interpolations, the path controlled is that of the center of rotation of the tool. Compensation for different tools, different diameter tools, or tool wear during machining, can be made in the NC program. 沿着路径的运动或以增量差

17、补是几个基本方式的一个,在所有的差补中,要控制刀具的回转中心定位,补偿可以以不同直径及刀具磨损,在数控程序中进行改写。 There are a number of interpolation schemes that have been developed to deal with the various problems that are encountered in generating a smooth continuous path with a contouring-type NC system. They include: 有一些已形成差补方案来处理数控系统中连续路径和加工系统产生

18、的问题包括: Linear interpolation线性差补 Circular interpolation圆弧差补 Helical interpolation螺旋线差补 Parabolic interpolation抛物线差补 Cubic interpolation立体差补Each of these interpolation procedures permits the programmer (or operator) to generate machine instructions for linear or curvilinear paths, using a relatively f

19、ew input parameters. The interpolation module in the MCU performs the calculations and directs the tool along the path. 每一种差补程序都允许程序源产生加工指令,适用于相对少的输入参数的直线或曲线路径。储存在数控单元中的模块预算指引工具沿计算出的路径运动 Linear interpolation is the most basic and is used when a straight-line path is to be generated in continuous-pat

20、h NC. 线性差补是最基本的差补方法,用于连续路径的数控系统中。 Two-axis and three-axis linear interpolation routines are sometimes distinguished in practice, but conceptually they are the same. The programmer is required to specify the beginning point and end point of the straight line, and the feed rate that is to be followed

21、along the straight line. 两轴和三轴线性差补路线在实际中有时会分辨出的,但在概念上他们是一样的,程序源要明确指定直线的起点和缺点及沿直线的进给率。The interpolator computes the feed rates for each of the two (or three) axis in order to achieve the specified feed rate. 差补需计算两轴或三轴的进给速率以达到设定的进给速度。Linear interpolation for creating a circular path would be quite in

22、appropriate because the programmer would be required to specify the line segments and their respective end points that are to be used to approximate the circle. 线性差补用来差补圆是不合适的因为程序源需要明确指定线段部分(线段数量)和各自的终点来大约模拟圆弧。Circular interpolation schemes have been developed that permit the programming of a path c

23、onsisting of a circular arc by specifying the following parameters of the arc: the coordinates of its end points, the coordinates of its center, its radius, and the direction of the cutter along the arc. 使用圆弧只要给定以下参数,圆弧终点坐标,圆心坐标,半径和刀具沿圆弧路径的走刀方向。The tool path that is created consists of a series of s

24、traight-line segments, but the segments are calculated by the interpolation module rather than the programmer. 向。圆弧差补也是由许多小的直线段来实现的,但这些小线段的参数由差补模块来计算出来的,而不是程序员设定的。The cutter is directed to move along each line segment one by one in order to generate the smooth circular path. 切削是沿着每一小线段一个一个的进行以产生光滑曲线

25、路径。 A limitation of circular interpolation is that the plane in which the circular are exists must be a plane defined by two axes of the NC system. 圆弧差补的局限性是圆弧路径所在平面是由数控系统中两轴所决定的平面。Helical interpolation combines the circular interpolation scheme for two axes described above with linear movement of a

26、 third axis. This permits the definition of a helical path in three-dimensional space. 螺旋线差补结合了环形差补两轴在第三轴上做线性运动这样来定义空间三维螺旋路径。Parabolic and cubic interpolation routines are used to provide approximations of free-form curves using higher-order equations. 抛物线差补和立方差补法通过高次高程来实现自由曲线。 They generally requir

27、e considerable computational power and are not as common as linear and circular interpolation. 这通常需要有强的计算能力,正因如此,他不如直线差补和环形差补常见。Their applications are concentrated in the automobile industry for fabricating dies for car body panels styled with free-form designs that cannot accurately and convenientl

28、y be approximated by combining linear and circular interpolations. 他们主要用于汽车工业中具有自由风格的车身面,而这是线性差补和圆弧差补不能精确容易得到的The most common application of numerical control is for machine tool control. This was the first application of NC and is today the most important commercially. 数控技术运用于数控机床,这是数控的主要应用。现在主要用于商

29、业。 In this section we discuss the machine tool applications of NC with emphasis on metal machining. 我们仍讨论数控系统特别是金属数控车床。 Machine Tool Technology for NC 数控车床技术Each of the five machining processes is carried out on a machine tool designed to perform that process. Turning is performed on a lathe, drilli

30、ng is done on a drill press, milling on a milling machining, and so on. 每种加工过程都可以在设计的专门车床上来实现加工。在车床上车削,在钻床上钻,在铣床上加工。 There are several different type of grinding operations with a corresponding variety of machines to perform them. 有几种类型的磨削方法也要有相应种类的磨床。Numerical control machine tools have been design

31、ed for nearly all of the machining processes. The list includes: 被设计的数控磨床可以进行下列加工包括: Drill presses钻加工 Milling machines, vertical spindle and horizontal spindle铣床立式和卧式主轴 Turning machines, both horizontal axis and vertical axis车床卧式主轴和立式主轴 Horizontal and vertical boring mills卧式和立式镗床 Profiling and conto

32、uring mills仿形铣床 Surface grinders and cylindrical grinders平面磨和圆柱磨 In addition to the machining process, NC machine tools have also been developed for other metalworking processes. These machines include: 除了上述几种机械加工方法,数控机床可用于其他金属加工过程包括: Punch presses for sheet metal hole punching用于薄片板的金属板上冲孔的冲压机 Presses for sheet metal bending用于薄片金属弯曲的折弯机。The introduction of numerical control has had a pronounced influence on the design and operation of machine tools. 数控技术的介入到机加工对机床的设计和运用有着显著的影响。One of the effects of NC has been that the proportion of time spent by the machine cutting me

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